This invention refers to an ion particle classifier and a method for classifying coarse solid particles from an air suspension of microized particles.
All industrial fields from medical industry to mine- and building material industry use as raw materials a continuously increasing amount of different types of micronized powder like dry products. The micronizing of these products is nowadays generally carried out in jet mills, in which highly pressurized air or overheated water vapor is generally used as grinding energy. Depending on the final product and the fineness thereof the energy consumption of these grinding and classifying processes is about 100 to 3000 kWh/ton.
At this moment a micronizing technique operating according to the opposed jet mill principle is considered to be the most effective and the most economic micronizing method. However, a wider utilization and application of the developed opposed jet mill technique has been considerably disturbed by the lack of effective auxiliary techniques applicable in connection with the opposed jet mill technique and/or their low efficiency and high energy costs.
Previously known micronizing devices and methods are especially affected with the below presented basic problems and shortcomings, which undoubtedly will cause a lot of unnecessary energy consumption and will limit the quality of the final products. Said shortcomings will also considerably limit an effective realization of the basic idea of opposed jet grinding.
In micronizing a high-energy power gas, most oftenly pressurized air, is used as grinding energy. The micronizing devices will need industrial compressor effects ranging from 100 kW to 1000 kW depending upon application.
Classifying of a product micronized in an opposed jet mill as well as the methods and the devices previously used to separate power gas and solids from each other, are affected by big technical shortcomings. In the separation of solids and power gas from each other, methods and devices using different kinds of filler fabrics have been utilized, which are affected by often appearing obstruction and eillux problems, as well as of an energy consumption caused by pressure differences and, without no exception, a centrifugal fan has to be used in all applications of the separation stage in order to develop pressure differences sufficient for the operation of the device. The finer final product is to be produced, the more expensive and more difficult to control will the classifying and the separation processes turn to be. In previously used grinding processes, wherein the size of particles to be treated was more than 5 xcexcm, such a problem did not appear.
The classifying has been based on centrifugal forces arising as a result of flow rate of a power gas and solids suspension and possibly of rate of rotation of a rotor mounted in a conventional classifying device. Control of a classifying process has been carried out by regulating the rate of rotation of said rotor as well as of the flow rate of the suspension of power gas and solids through the classifier during an initial stage of the classifying procedure, but no continuous regulation has been carried out.
It is therefore, an object of the present invention to eliminate the above drawbacks by providing a new and improved ion particle classifier.
It is another object of the present invention to provide a new and improved classifying method for separating coarse particles from an air suspension of micronized particles.
In accordance with the present invention there is provided an ion particle classifier comprising a housing surrounding an electrically conductive, cylindrical inner layer, acting as a first electrode, and a centrally positioned electrically conductive rod with a number of radially directed tips, acting as a second electrode, said electrodes being electrically insulated from said housing and coupled to a high voltage current source, an inlet pipe for said air suspension of micronized particles to be classified terminates at one end of said first electrode and an outlet pipe for an air suspension of classified fine particles is mounted close to the opposed end of said first electrode, one end of said housing is provided with discharge means for a traction of classified coarse particles of said air suspension, said classifier further being provided with a rinsing air input entering said classifier at either end of said first electrode. The classifier can be vertical or horizontal.
By means of such an ion particle classifier a very sharp and effective classifying effect is achieved when flowing an air suspension of micronized particles to be classified at a low speed through a high voltage electrical field maintained in said classifier. The ion particle classifier according to this invention is very effective and requires considerably less energy in classifying micronized solids although having very small particles size than has been possible in previously known classifying devices.
In accordance with the invention there is also provided a classifying method for separating coarse particles from an air suspension of micronized solid particles, comprising the steps of flowing said air suspension of micronized particles at a low speed up through a high voltage electric field in a classifier, between a first outer cylinder electrode and a concentrically therewith positioned second inner rod shaped electrode having a number of radially directed tips, whereby coarse particles are attracted to the inner wall of said first electrode, fall down due to force of gravity and are removed by means of discharge means, the classification being regulated by adjusting the rate of the air suspension, the voltage of the electric field as well as by adjusting solid content of the air suspension flowing through the electric field by adding rinsing air.
By means of this invention the energy economy and the efficiency of the micronizing and classifying process can be considerably improved, the environmental load can be decreased, and special products with a higher fineness than earlier can be produced, e.g. a product having a fineness of even a nano level.
Further features of the invention will appear from the attached depending claims.